The invention relates to an analyzing method for a sensor system determining the position of a shifting fork in a change gear transmission.
In motor vehicles as a recent development automated shift transmissions are used in series. In these automated shift transmissions individual gears can be engaged for example by hydraulic or electric actuators. Typically, a gear is engaged by a shifting sleeve that correlates to the respective gear and is shifted in axial direction and thereby brought into positive interlocking with a loose wheel of the respective gear. The actuator is mechanically coupled with a shifting fork that is moved together with the shifting sleeve. The shifting fork can typically be moved from a neutral position into two opposite directions, namely one gear position in that one of the gears of the shift transmission is engaged and a further gear position in which another one of the gears of the shift transmission is engaged. For example, in a 7-gear-transmission the seven forward gears and the reverse gear can be engaged or disengaged by means of four shifting forks.
For controlling actuators for engaging and disengaging gears in the shift transmission it is necessary to determine the exact position of the respective shifting forks. From the prior art, respective sensor systems for determining the position are known. Among these sensor systems are also contactless sensor systems having a magnetic field sensor and a permanent magnet. For example, the magnetic field sensor in a shift transmission can be located at a fixed position, while the permanent magnet can be fixed to a movable shifting fork. The magnetic field sensor and permanent magnet are separated from each other by an air gap and are disposed with respect to each other such that the change of the position of the shifting fork moves the permanent magnet relative to the magnetic field sensor and therefore changes the magnetic field. The change in the magnetic field is detected by the magnetic field sensor so that the output signal changes. The output signal is finally analyzed for determining the position of the shifting fork.
In shift transmissions, due to production tolerances, air gaps of various sizes between the magnetic field sensor and the permanent magnet may result, influencing the level of the output signals of the magnetic field sensors. Further influencing parameters influencing the output signal are the magnetic flux strength of the magnet and the sensitivity of the magnetic field sensors, also due to production tolerances. In addition, further influencing parameters are present such as the temperature in the shift transmission and a possible deposition of chips at the magnet. The many influencing parameters make the detection of the position based on the output signal from the magnetic field sensors difficult.
The DE 101 24 760 A1 discloses a method for analyzing a sensor system comprising a magnetic field sensor and a permanent magnet. The DE 101 24 760 A1 suggests to analyze the non-linear output signal from the magnetic field sensors only over a certain operating range where the position change and the output signal correlate in a linear fashion with respect to each other. Further, according to the DE 101 24 760 A1 for a limited operating range by standardizing the output signals to a predetermined maximum signal deviation analyzing should be allowed that is allegedly independent from the temperature influences and the influence by the air gap.
In the DE 101 24 760 A1 a comparatively simple analysis is disclosed. The disadvantage is that the operating range is limited and for particular applications, for instance for determining the position of a shifting fork, can be too short. The DE 101 24 760 A1 suggests for enlarging the operating range to provide a plurality of the magnetic field sensors lined up in the direction of movement one after the other while the respective operating ranges of the individual magnetic field sensors overlap and therefore a larger overall operating range results. However, this increases the number of magnetic field sensors in the shift transmission and therefore costs.